Insulating composite materials comprising an inorganic aerogel and a melamine foam

ABSTRACT

The invention relates to insulating composite materials comprising an inorganic aerogel and a melamine foam. The invention also relates to the production method of said materials, and to the use of same.

The present invention relates to insulating composite materialscomprising an inorganic aerogel and a melamine foam, a process for theirmanufacture, and their uses.

Energy conservation, particularly with thermal insulation, is animportant issue in industry and building construction.

Traditional thermal insulation includes the use of glass wool, rock,extruded polystyrene or expanded polystyrene, often used in combinationin industrial insulation systems or building construction. For buildingconstruction, the insulation may be glued to plaster board.

The thermal insulation performance of insulation materials is measuredby their thermal conductivity. The lower the value of the thermalconductivity, the less the material conducts heat and the better thethermal insulation is. In the present invention, the thermalconductivity is measured by means of guarded hot plate according to NFEN 12667 standards (as of July 2001) at 20° C. and atmospheric pressure.

However, manufacturers are looking for ever more efficient and moreeconomical insulation materials.

It is in this context that insulation based on aerogels and xerogels hasbeen developed.

A gel has a continuous three-dimensional porous structure. Preparationof the gel involves a sol-gel transition step, that is to say thetransition of a suspension of solid particles (sol), to a gelatinoussolid (gel).

Gels are distinguished according to the nature of the fluid present inthe pores of the gel, xerogels and aerogels (air), hydrogels (water),organogels (organic solvent), and in particular the alcogels (alcohol).Hydrogels, alcogels and organogels are also gathered under the moregeneral term, lyogels.

Traditionally, the term aerogel refers generally to a gel dried undersupercritical conditions, that is to say that the majority of thesolvent is in the supercritical fluid state under these conditions;whereas the term xerogel refers to a gel dried under subcriticalconditions, that is to say that the majority of the solvent is not inthe supercritical fluid state under these conditions. Both aerogels andxerogels are very interesting not only for their excellence in thermalinsulation and acoustics, but also for their low density.

However, for simplification purposes, the term “aerogel” includes bothaerogels and xerogels.

Aerogels are typically obtained in granular form, which poses problemsin transportation and handling. Several solutions have thus emerged toobtain “monolithic” (reinforced) aerogels.

It is further advantageous, particularly for applications in buildingconstruction, to obtain a thickness of insulating material, for examplegreater than 2 cm, especially around 5 cm.

The new standards for insulation inside buildings (2012 French ThermalRegulations) advocate the use of panels whose thermal resistance is R=3m²K/W.

Another problem related to the use of aerogels, and particularlygranular aerogels is their dusting character; that is to say theyrelease dust, silica in the case of silica aerogels for example.

A first category of “monolithic” (reinforced) materials which overcomessome of these problems is obtained by adding a binder to a particulateaerogel. Aerogels particles are thus “glued” together. The use of foamsas a binder is one general way of improving thermal performance of thematerial used. This is what has been described in US 2012/0142802, EP1808454, EP 0340707 and DE 19533564, in which the binder is a melaminefoam.

A process for preparing this type of monolithic composite materialconsists of mixing the aerogel particles in a preformed mixture ofmelamine foam precursors, and carrying out a polymerization reaction andformation of the foam. The materials obtained according to such amethod, however, have average thermal insulation performance (thermalconductivity in general between 25 and 40 mW/m-K). In particular,document US 2012/0142802 teaches the use of a foam having a pore sizebetween 10 and 1000 μM, and an aerogel with a pore size less than 50 nmand a porosity of between 50 and 99% as starting materials.

However, although US 2012/0142802 indicates that the obtained compositematerials can have a thermal conductivity of between 10 and 100 mK/m-K,preferably between 15 and 40 mK/m-K (see [00139]), the reference onlyenables composites of thermal conductivity greater than 22 mK/m-K (seeExamples 1 and 5), regardless of the content of the aerogel material(62% for example 1 and 94% for Example 5). Furthermore, US 2012/0142802does not specify the macroporosity of the composite materials obtained.EP 1808454, EP 0340707 and DE 19533564 also do not specify thesecharacteristics. Patent application US 2012/0064287 teaches monolithiccomposite materials comprising a support, comprising amelamine-formaldehyde copolymer with a plurality of micropores, and anaerogel matrix disposed in the micropores (see abstract and [0010]). Theaerogel matrix can be made of an organic aerogel such as acrylamideaerogel, benzoxazine, bis-maleimide, of aryl alcohol, cellulose,benzaldehyde substituted by hydroxy, or an inorganic aerogel, e.g.silica, or a combination thereof (see [0011] and [0156]). Application US2012/0064287 expands at length on matrices of organic aerogels,including consideration of several formulas for the precursors of theorganic aerogels. However, it provides no details on their structure,particularly regarding their macroporosity. Moreover, none of theexamples relate to a composite material comprising an inorganic aerogel.

Meanwhile, the documents US 2007/0259979, US 2009/0029147 and U.S. Pat.No. 6,040,375 disclose composites comprising an open cell foam, inparticular polyurethane foam combined with a silica aerogel, obtainableby casting a silica sol in a preformed polyurethane foam panel, followedby gelling, and drying. The resulting materials have a thermalconductivity of between 18 and 22 mW/m-K. The document US 2009/0029147seems to teach that the obtained aerogel has a porosity of at least 95%.Other documents do not seem to characterize the pore diameter orporosity of the materials.

Thus, the skilled person is not inclined to develop a composite materialbased aerogel and melamine foam, since melamine foam, according to thedisclosures of the prior art, appear to be not very efficient in termsof thermal insulation, particularly compared with otherpolyurethane-based foam materials. It is further discouraging that thethermal conductivity of melamine foams, including foams Basotectmarketed by BASF, is about 35 mW/m-K, while the thermal conductivityopen cell polyurethane foams is generally between 20 and 25 mW/m-K.

Surprisingly, the applicant has made composite insulating materialscomprising an inorganic aerogel and an open-cell melamine foam havinggood thermal insulation performance which are easy to handle, and havegreatly decreased (even eliminated) dusting character. The foam does notplay the role of binder in these composites.

Within the context of the present invention, the term “aerogel” includesboth aerogels and xerogels.

Within the context of the present invention, the term “compositematerial” is understood as a material comprising at least two immisciblecompounds intimately related. The composite material has properties,including physical (e.g. thermal conductivity, stiffness, etc), thateach of the materials taken separately do not necessarily have.

Within the context of the present invention, the term “monolithic” isunderstood as a material or aerogel which is solid and is in the form ofa single block piece, particularly in the form of a panel. Themonolithic aerogel material can be flexible or rigid.

The term “rigid” is meant that the material cannot be significantlydeformed without observing the formation of cracks or rupture in themonolithic material. In particular, this means that the monolithicmaterial cannot be rolled. The term “flexible” is meant that thematerial can be deformed, in particular wound. The term“self-supporting” can also be used to qualify monolithic material inwhich the product stability is not due to an external support. Aself-supporting monolithic material can be flexible as well as rigid.

Within the context of the present invention, the term “foam” isunderstood as substance, including a polymer, trapping gas bubbles init. Foams can be a “closed cell foam”, that is to say that a majority ofthe gas pockets are completely enclosed with the solid material, asopposed to “open cell foams”, wherein a majority of the gas pockets areopen to each other. For example, foam marketed under the name ofBasotect® are open cell foams.

Within the context of the present invention, the term “melamine foam” isa foam comprising a polymer whose monomer is a melamine. An example ofmelamine foam is a melamine-formaldehyde foam, from a polymerizationreaction between melamine and formaldehyde.

Within the context of the present invention, the term “macropore” isunderstood as a pores with a diameter greater than 10 μm.

Within the context of the present invention, the term “total macropore”is the total number of pores with a diameter greater than 10 μm.

Within the context of the present invention, the term “macroporosity” ofa porous material is the ratio of the volume occupied by the macroporesin the volume occupied by the material in its entirety. Themacroporosity is expressed in percentage (%) and measured by threedimensional (3D) X-ray tomography. Preferably, X-ray tomographyacquisitions are made using the DeskTom machine model with a 130 kVgenerator. The distance from source to sample is about 12 cm. Thesoftware used for the acquisition and reconstruction of the data is theX-Act program developed by RX Solutions. For post-processing(visualization and analysis of porosity), the software VG Studio MaxVersion 2.2 was used. The settings can be established according to thegeneral knowledge of a skilled person.

Within the context of the present invention, the term “diameter” candescribe the pores of a porous material, with the diameter determined bya statistical extrapolation of the macropore volume distribution of theporous material, for example as measured by three dimensional (3D) X-raytomography. It is believed that the pores are in the shape of a sphere.The relationship between the diameter of the macropores and the volumeof the material is as follows: V=(pi×D³)/6, with V as the volume and Das the diameter of the sphere. One example of determining the porediameter for materials of the present invention is presented in Example1.

Without being bound to this specific interpretation, it seems that theproperties of the composite material according to the invention, andespecially the low thermal conductivity, are intrinsically linked to themacroporosity of the material. Thus, the remarkable thermal performanceof materials according to the invention are the result of the control ofthe macroporosity of the material and/or diameter of the macropores.

The presence of macropores effects the overall thermal conductivity bygenerating a contribution to conductivity by significant gas convection.Minimization of the proportional volume of macropores with respect tototal volume can produce remarkable thermal performance.

Indeed, as Knudsen formalism quantifies, the thermal conductivity of theair depending on the characteristic confinement dimension (eg poresize), λ increases according to the following law:

${\lambda_{g\; 6} = \frac{\lambda_{0}}{1 + {\alpha \; K_{n}}}},$

wherein λ0 the conductivity of free gas (ie unconfined) is theaccommodation coefficient between the gas and the solid (coefficientreflecting the quality of heat exchange between the gas and theconfining solid); Kn, the Knudsen factor, defined as the ratio betweenthe free mean path of the gas and the characteristic dimension of thecontainment (eg pore size).

Thus, over a macropore size of 10 μm, air is no longer confined, whichnegatively influences the thermal conductivity properties.

An object of the present invention is to provide a monolithic compositematerial comprising an inorganic aerogel and a melamine foam with opencells, said material having a thermal conductivity λ between 5 and 20mW/m-K, measured according to the guarded hot plate method of thestandard NF EN 12667 at 20° C. and atmospheric pressure, and having amacroporosity of less than 5%, preferably less than 2%.

Another object of the invention relates to a method of manufacturing amonolithic composite material comprising an inorganic aerogel and anopen-cell melamine foam according to the invention, comprising thefollowing successive steps: a) casting an inorganic sol in a reactor inwhich a preformed open-cell melamine foam has been placed beforehand, b)gelation of the sol into a lyogel, c) drying the lyogel.

For the purposes of this invention, hydrogels, alcogels and organogelsare also gathered under the more general term, lyogels.

Another object of the invention relates to a monolithic compositematerial comprising an inorganic aerogel and a melamine foam, saidmaterial having a thermal conductivity λ between 5 and 20 mW/m-Kmeasured according to the guarded hot plate method of the NF EN 12667 at20° C. and atmospheric pressure, and obtainable by a method according tothe invention.

Another object of the invention relates to a multilayer panel comprisingat least one layer consisting essentially of a composite materialaccording to the invention.

Another object of the invention relates to the use of a monolithiccomposite material comprising an inorganic aerogel and an open-cellmelamine foam, or a multilayer panel according to the invention, asthermal or acoustic insulator.

Composite Material

The present invention relates to a monolithic composite materialcomprising or consisting essentially of an inorganic aerogel reinforcedby a pre-formed open-cell melamine foam, said material having a thermalconductivity λ between 5 and 20 mW/m-K, preferably between 10 and 20mW/m-K, advantageously between 10 and 15 mW/m-K, measured according tothe method of the guarded hot plate of the standard NF EN 12667 at 20°C. and atmospheric pressure, and having a macroporosity of less than 5%,preferably less than 2%.

In the context of the present invention, the term “consistingessentially of” is meant that the material may include other elementsthan those mentioned, but sufficiently small quantities that they do notalter the essential characteristics of the material. Thus, the materialmay contain impurities, including trace impurities.

The monolithic composite material of the invention is monolayer. Thematerial is also observed to be homogeneous, especially in terms ofstructure, thermal conductivity, macroporosity and flexibility.

Melamine foam improves certain mechanical properties of the aerogel,while maintaining a thermal conductivity less than 20 mW/m-K measured bymeans of guarded hot plate of NF EN 12667 at 20° C. and atmosphericpressure. For example, the maximum stress in elastic phase of thecomposites is much larger than that of the corresponding non-reinforcedaerogel. Typical values are 3.5 MPa respectively (for the compositematerial) and 1·10⁻⁴ MPa (for the corresponding non-reinforced aerogel).

Within the context of the present invention, the term “preformed foam”is meant that the open-cell melamine foam no longer undergoes chemicalreaction changing the melamine polymer structure, including chemicalpolymerization reaction or crosslinking. Moreover, the macroporosity ofthe foam is not changed by a physical reaction. The only alteration thatthe foam is subject to is the formation of the gel within its opencells. The shape of the resulting composite material will be essentiallyidentical to that of the preformed foam.

Advantageously, the thermal conductivity measured by means of guardedhot plate of the NF EN 12667 at 20° C. and at atmospheric pressure isbetween 5 and 20 mW/m-K, even more preferably between 8 and 15 mW/m-K.

It is found experimentally that the material of the invention has poreswhose diameter is between 50 and 250 μm.

Preferably, macropores having a diameter between 50 and 250 micronscomprise more than 80% (by number) of the total number of macropores(pores having a diameter greater than or equal to 10 μm) of the materialaccording to the invention.

Preferably, the open-cell melamine foam is melamine-formaldehyde. Oneexample of a melamine-formaldehyde foam is Basotect foam marketed byBASF. In a particular embodiment, the melamine-formaldehyde foam has athickness between 2 and 50 mm, a porosity of between 95% and 99.5%, adensity between 8.5 and 11.5 kg/m³ and a thermal conductivity between 35and 40 mW/m-K measured by means of guarded hot plate of NF EN 12667 at20° C. and atmospheric pressure.

The melamine foam provides structure the aerogel to improve itsmechanical strength properties and resistance, while retaining itsthermal insulation properties.

Advantageously, the composite material of the invention has a densitybetween 70 kg/m³ and 150 kg/m³, preferably between 100 and 120 kg/m³.

Preferably, the composite material according to the invention comprisesbetween 85% and 98% by weight aerogel based on the weight of thecomposite material, preferably between 90% and 95%, between 92% and 98%,or between 92 and 95% by weight aerogel based on the total weight of thecomposite.

Advantageously, the inorganic aerogel is selected from silica aerogels,titanium oxide, manganese oxide, calcium oxide, calcium carbonate,zirconium oxide, or mixtures thereof, preferably from silica aerogels.

In an one advantageous embodiment, the composite material according tothe invention has a thickness between 2 and 50 mm, preferably between 5and 30 mm, for example between 10 and 20 mm. It is observed that thethickness of the monolithic composite material is correlated with thethickness of the melamine foam used. Thus, the melamine foam preferablyhas a thickness between 2 and 50 mm, preferably between 5 and 30 mm, forexample between 10 and 20 mm.

The aerogel may further include an additive. Advantageously, theadditive is intended to improve the mechanical properties, cohesion, orthermal conductivity of monolithic composite materials according to theinvention. Preferably, the additive comprises an opacifier. Thus,advantageously, the material of the invention further comprises anopacifier. The use of an opacifier makes it possible to decrease thevalue of the thermal conductivity by reducing its radiative component.Typically, the opacifier is selected from SiC, TiO₂, carbon black,graphite, ZrO₂, ZnO, SnO₂, MnO, NiO, TiC, WC, ZrSiO₄, Fe₂O₃, Fe₃O₄,FeTiO₃. In particular, the opacifier is selected from the groupconsisting of SiC and TiO₂.

In a preferred embodiment, the composite material according to theinvention comprises no binder. Examples of inorganic binders includecements, plasters, gypsum, lime; and examples of organic binders includethermoplastic polyolefins such as waxes, styrene polymers, polyamides.The term “binder” also includes adhesives, such as epoxy resins andcyanoacrylates, for example.

In a preferred embodiment, the composite material of the invention doesnot comprise a fibrous reinforcing material. For the purposes of thepresent invention, a “fibrous reinforcing material” includes fibers or anonwoven fibrous web, or a mixture thereof. The various types of fibersadapted for the manufacture of thermal insulation are known to thoseskilled in the art. Examples include glass fibers, mineral fibers,polyester fibers, aramid fibers, nylon fibers and vegetable fibers, or amixture thereof, as described in U.S. Pat. No. 6,887,563.

Advantageously, the composite material according to the invention ishydrophobic, vapor permeable, and stable at temperatures up to 250° C.It cuts easily and has minimal dust compared to other compositematerials based on silica aerogel. In addition, composites of theinvention are lightweight and flexible. They also exhibit good acousticinsulation properties. The materials according to the invention havegood fire resistance properties, they are preferably classified at leastB1 according to German DIN 4102-1, Ml in France according to the NFP-92507 or V0 according to the United States UL94. The combustion energyor gross calorific value of the composite material according to theinvention measured according to standard NF EN ISO 1716 is preferablylower than most performance insulating materials such as polyurethane.

The material according to the invention is obtainable by the processcomprising the following successive steps: a) casting an inorganic solin a reactor in which was first placed a preformed open-cell melaminefoam, said sol comprising preferably more than 5% by weight, morepreferably between 6 and 15% by weight, of inorganic material based onthe total weight of the sol, b) gelation of the sol into a lyogel, c)drying the lyogel under subcritical conditions.

A method for obtaining materials according to the invention is describedin more detail hereinafter.

In the present invention, the quantity of residual solvent by weight ofthe monolithic composite material is calculated according to EN/ISO3251. The protocol used involves taking 1 g of aerogel according to theinvention, weighing, and then drying for 3 hours in an oven at 105° C.,then weighing the dried aerogel.

The composite material according to the invention typically has aquantity of residual solvent by weight of the composite material lessthan or equal to 3%, preferably less than 1% in accordance with EN/ISO3251.

Multilayer Boards

The present invention also relates to multi-layer panels, in particularin the form of multilayer laminates or sandwich panels comprising atleast one layer consisting essentially of a monolithic compositematerial of the invention, optionally in combination with layers ofdifferent materials.

In the multilayer panel according to the invention, each layer is madeof a monolithic material or a panel adhered to one or more other layers.For example, one or more plasterboard (optionally type BAI13) may bebonded to one or each side of a monolithic composite material of theinvention to form a wall covering. Also contemplated are multi-layercomposite panels comprising a combination of one or more compositematerials according to the invention and a composite material asdescribed for example in international application WO 2013/053951.

The composite material according to the present invention provides amultilayered panel with improved characteristics suitable for specialapplications. For example, a monolithic composite material of theinvention laminated to a rigid insulation panel according to applicationWO 2013/053951 provides a compressive elasticity or acoustic dampingsuperior to the individual material. The layer made of the monolithiccomposite material of the invention can also act as a firewall or flameretardant or high temperature insulation layer relative to the materialwhich it is associated.

Laminating a composite layer of thermoformable material between twolayers of the multilayer panel can confer the laminate an ability to bethermorformed itself.

Process for Obtaining

The present invention also relates to a method for producing amonolithic composite material comprising or consisting essentially of aninorganic aerogel reinforced by a pre-formed open-cell melamine foamhaving a thermal conductivity λ between 5 and 20 mW/m-K measured bymeans of guarded hot plate of the standard NF EN 12667 at 20° C. andatmospheric pressure, and having a macroporosity of less than 5%,preferably below 2%, comprising the following successive steps: a)casting an inorganic sol in a reactor in which was first placed apreformed open-cell melamine foam, said sol comprising preferably morethan 5% by weight, more preferably between 6 and 15% by weight,inorganic material relative to the total weight of the sol, b) gelationof the sol into a lyogel, c) drying the lyogel.

The drying in step c) is preferably carried out so that the obtainedaerogel has a quantity of residual solvent by weight of the compositematerial of less than or equal to 3%, preferably 1%, in accordance withEN/ISO 3251. Advantageously, the drying step c) takes place undersubcritical conditions.

Advantageously, binder, in particular as defined above, is not used oradded in any step of the process according to the invention.Furthermore, preferably no fibrous reinforcing material, as definedabove, is employed in the process according to the invention.

Preferably, the sol used in step a) is selected from the group of silicasols, titanium oxide, manganese oxide, calcium oxide, calcium carbonate,zirconium oxide or mixtures thereof. Preferably, the sol is a silicasol. Thus, step a) preferably comprises the casting of a silica sol in areactor in which was first placed a preformed open-cell melamine foam,said sol comprising preferably more than 5% by weight, more preferablybetween 6 and 15% by weight of silica based on the total weight of sol.More preferably, the silica sol comprises between 6 and 10% by weight ofsilica based on the total weight of soil.

An additive may be added to the sol in step a), preferably an additivecomprising an opacifier. The additive and the opacifier are as definedabove.

The sol used in step a) is obtained for example by acid or basecatalysis of a silica precursor in the presence of a catalyst. Thetransformation of the silica sol to lyogel (gelation step b) is carriedout preferably in the presence of a gelling catalyst, such as ammonia.Advantageously, the catalyst is used at a concentration of between 1 and3%, preferably between 2 and 2.5% by weight based on the total weight ofthe starting sol, ie including the solvent, the silica precursor andoptional additives.

The lyogel obtained in step b) preferably comprises from 70 to 90%>byweight of solvent, preferably from 75% to 85% by weight solvent, basedon the starting weight of soil. More preferably, the lyogel obtained instep b) preferably comprises from 85 to 94% solvent by weight,preferably from 90% to 94% by weight of solvent, based on the startingweight of sol.

The skilled person will adjust the reaction conditions of step b)gelling, and particularly the gelling time, so as to obtain a uniformlyimpregnate the preformed foam with the silica gel, which ensures theprovision of a macroporosity of less than 5% for obtaining a thermalconductivity λ between 5 and 20 mW/m-K measured by means of guarded hotplate of NF EN 12667 at 20° C. and atmospheric pressure.

PARTICULAR EMBODIMENTS Step b)

In one embodiment, the lyogel is an alcogel. In this case, the solventis preferably ethanol. In this embodiment, step b) is advantageouslyfollowed by a step b2) aging the alcogel followed by a step b3)hydrophobizing treatment of the alcogel, after which a hydrophobicalcogel is obtained. Step b2) includes, for example contacting thealcogel obtained in step b1) with a hydrophobizing agent in acid mediumof pH of between 1 and 3. Advantageously, the hydrophobizing agent usedis selected from the group of organo-siloxanes, organo-chlorosilanes ororgano-alkoxysilanes, more advantageously, the hydrophobizing agent usedis selected from the group consisting of hexamethyl-disiloxane (HMDSO),trimethyl-chlorosilane and trimethyl-ethoxysilane, even moreadvantageous hexamethyl-disiloxane (HMDSO). In addition, in thisembodiment, the silica sol according to the invention is preferablyobtained by controlled hydrolysis of tetraethoxysilane in ethanol.Advantageously, the ethanol generated during the hydrolysis is recycledand reused as solvent the same step subsequently. Preferably, step b3)comprises contacting the alcogel obtained in step c) with ahydrophobizing agent in acid medium of pH of between 1 and 3.

Advantageously, the alcogel is acidified in step b3) by addition of amineral or organic acid. More desirably, the inorganic acid ishydrochloric acid and the organic acid is trifluoroacetic acid. Evenmore advantageously, the acid is trifluoroacetic acid or hydrochloricacid, and hydrophobing agent hexamethyldisiloxane (HMDSO).Advantageously, step b3) is conducted at a temperature between 50° C.and 150° C. Even more preferably, step b3) is conducted at the alcoholboiling temperature (solvent of the alcogel). In the case where thesolvent is ethanol, step b3) is carried out under reflux of ethanol.

In another embodiment, the lyogel obtained at the end of step a) is ahydrogel. In this case, step b) is advantageously followed by a step b2)exchange of the solvent (water) with an organic solvent such as acetone,hexane or heptane leading to the formation of a lyogel, the stepoptionally preceded by a step of aging the hydrogel, and followed by astep b3) hydrophobizing treatment of the lyogel, after which ahydrophobized lyogel is obtained. In cases where the lyogel is ahydrogel, The implementation conditions of step b3) hydrophobizingtreatment of the lyogel are similar to those described above (inparticular temperature, reactants, etc.) near the solvent.

In the previous embodiments, the aging step improves mechanicalproperties of the lyogel due to the effects of syneresis (separation ofthe liquid and the gel). This aging step preferably has a duration ofless than 24 hours. Conditions such as temperature and aging time can beset according to criteria known to those skilled in the art such as, forexample, the composition of the gel. Advantageously, the aging step isconducted at a temperature between 40° C. and 80° C., even morepreferably at a temperature between 45° C. and 60° C. Advantageously,the aging step has a duration less than 20 h.

In the previous embodiments, the hydrophobic treatment in step b3) ofthe process allows for reduction of the water uptake of the compositematerial. The composite material according to the invention preferablyhas a water uptake rate at room temperature and 75% relative humidity ofless than 5%, more preferably less than 3% and preferably a waterrecovery ratio at room temperature and 95% of less than 10%, even morepreferably less than 5%.

PARTICULAR EMBODIMENTS Step c)

In one embodiment, step c) is divided into a step c1) of pre-curing insubcritical conditions at a temperature below 80° C., and a step c2) ofdrying under subcritical conditions, said drying step c2) beingdielectric or convective, at a temperature above 100° C. when saiddrying c2) is convective.

In one embodiment, step c2) is a convective drying, performed at atemperature between 120° C. and 180° C., preferably between 140° C. and160° C., even more preferably equal to about 150° C. The convectivedrying can be conducted in a natural fashion, but is preferably carriedout in forced convection mode.

In another embodiment, step c2) is a dielectric drying step bymicrowaves.

Preferably, the pre-drying step c1) is continued until a condensedlyogel is formed, having lost between 10 and 80% alcohol by weight,preferably between 20% and 60% by weight of alcohol, even morepreferably between 40% and 50% by weight alcohol based on the weight ofthe starting materials.

Advantageously, the pre-drying temperature in step c1) is between 40° C.and 80° C., even more preferably between 60° C. and 80° C., even morepreferably equal to about 80° C.

In a preferred embodiment of the invention, the step c1) is performed bycirculating a hot gas stream in the reactor. The gas stream is typicallya flow of inert gas such as nitrogen, air or a noble gas.Advantageously, the hot gas stream flows vertically, even morepreferably from top to bottom.

In another embodiment, the pre-drying in step c1) is conducted underreduced pressure. Such an embodiment is advantageous because it allowsfor shorter pre-drying times at the same temperature.

Advantageously, step c2) is performed by convective drying bycirculating a stream of hot air into the dryer. At the laboratory scale,the convective drying is preferably carried out in an oven at atemperature of 150° C.

In another embodiment, step c2) is carried out by dielectric drying bymicrowaves. Preferably, the power supplied in the microwave drying stepis between 0.3 kW and 3 kW per kg of starting condensed lyogel,preferably between 0.5 kW and 2 kW per kg of condensed lyogel, stillpreferably equal to about 1 kW per kg of condensed lyogel. Said power isadjusted during the drying so that the material surface temperature isbetween 40° C. and 400° C., more preferably between 40° C. and 200° C.,even more preferably between 50° C. and 150° C.

The mass of solvent lost during step c) or C1) is measured differentlydepending on the scale of the process. At the laboratory scale, thisquantity is measured by weighing the lyogel obtained after step b)before and after drying under the conditions of step c) or c1). On anindustrial scale, the solvent evaporated during the drying step c) orC1) is condensed in another reactor, and then weighed.

PARTICULAR EMBODIMENT The Nature of the Reactor

Advantageously, at least steps a), b) and c1) are implemented in atleast one reactor, with a characteristic distance of said reactorbetween two inner walls comprising between 2 mm and 50 mm, preferablybetween 5 to 30 mm. This feature of reactor improves the diffusion ofthe reactants to the core of the composite material so that thecomposition of the composite material is homogeneous.

Within the context of the present invention, the term “inner wall of thereactor” is meant the wall which is in direct contact with thereactants. For example, in the case of a jacketed reactor, it is thewall of the inner shell in direct contact with the reactants. Within thecontext of the present invention, the term “characteristic distancebetween two inner walls” is meant the maximum distance between twoparallel inner walls, or between the surface tangent to one of said thewalls and a wall parallel to the latter, or between two surfaces tangentto the wall. For example, in the case of a cylindrical reactor, thecharacteristic distances between two internal walls of the reactor arethe internal diameter and the internal height of the reactor. In thecase of a cubic reactor, the characteristic distance between two innerwalls of the reactor is the inner side of the cube. In the case of arectangular reactor, the characteristic distances between two internalwalls of the reactor are the internal height, the internal length andinternal width. Preferably, the characteristic distance between twoinner walls is chosen from the height, width, length, thickness andinternal diameter.

Due to the particular geometry of the reactor, the distance from anypoint within the reactor to the inner wall of said reactor is such thatthe diffusion of the reactants into the lyogel is optimal. In addition,such a reactor also allows for optimized conditions of pre-drying thelyogel in step c1), if carried out in such a reactor.

Thus, steps a), b) and c1) are advantageously carried out in a firstreactor, then the condensed lyogel is removed and transferred to aconvective or dielectric drying reactor for step c2).

Within the context of the present invention, the term “drying” is meantas reactor for the implementation of a drying step.

Applications

The present invention also relates to the use of a composite material orof a multilayer panel according to the invention, as thermal insulation,in particular for applications in building construction or in theinsulation of industrial systems or methods.

Thus, composite materials or multi-layer panels according to theinvention are advantageously used for the manufacture of constructionmaterials, including walls and partitions but also floors or ceilings orfor insulating industrial piping.

The multilayer composite materials and panels according to the presentinvention may also be used as acoustic insulators.

DESCRIPTION OF FIGURES

FIG. 1: Distribution of the macropore volume measured by X-raytomography in three dimensions (3D) on the composite material obtainedin Example 1. The x-axis represents the volume in mm³ (on a scale of 0to 0.01 mm³) and the y-axis represents the number of macropores (on ascale from 0 to 250). The mean pore volume (Vm) for a vast majority ofthe material was between 1·10⁻⁴ mm³ and 5·10⁻³ mm³.

FIG. 2: A diagram showing the three-point bending device for measuringthe flexibility modulus of a material. The panel is placed on twosupports (represented by triangles) located at 7.5 cm from the edge, andspaced 10 cm apart, and a vertical downward force is applied bypositioning the various weights (represented by a sphere in the Figure)placed at the center of the material. The distance from the center ofdeformation of the material is measured.

FIG. 3: Curve representing the force (measured in Newton (N), y-axis) asa function of the flex (measured in mm, x-axis). This curve representsthe test results of Example 3. Linear regression is used to determine aslope of 0.0385 N/mm, and an intercept of 0.

FIG. 4: Representation of the test results of Example 4. The curveobtained represents the conventional stress (expressed in MPa) asfunction of the relative deformation, ∈=(e−e₀)/e₀, with e₀ as the samplethickness before the test, and ∈ being without units.

The examples which follow are intended to further illustrate the presentinvention but are in no way limiting.

EXAMPLES Example 1 Preparation of a Composite Panel of Thickness 10 mmAccording to the Invention 1) Preparation of a Silica Alcogel Composite

A silica sol obtained by hydrolyzing alkoxysilane in the presence ofhydrochloric acid and then adding ammonia, was poured before gelation ona 250×290×10 mm³ sheet of melamine foam (Basotect foam marketed by BASF)in a closed chamber 300×300×70 mm³ in dimensions. After gelling, thereinforced alcogel was aged for 24 hours at 50° C. in ethanol.Hydrochloric acid and hexamethyldisiloxane (hydrophobing agent) werethen introduced into the chamber to completely cover the compositealcogel. The reaction medium was heated and maintained at 50° C. for 48h. The reaction mixture was separated from the hydrophobic silicaalcogel composite by percolation.

2) Production of a Composite Material Comprising Melamine Foam andHydrophobic Silica Aerogel

The condensed alcogel reinforced by the melamine foam sheet was dried ina ventilated oven at 160° C. for 2 hours. The aerogel panel obtained is10 mm thick and has a thermal conductivity of 12.6 mW/m-K, measured bymeans of guarded hot plate of NF EN 12667 at 20° C. and atmosphericpressure.

3) Measurement of Pore Diameter and Macroporosity

The composite material obtained after drying is then analyzed by 3DX-ray tomography. The acquisitions were made with DeskTom machine modelequipped with a 130 kV generator. The resolution obtained on the sampleis 24.5 μm, with a source/sample distance of about 12 cm. The softwareused for the acquisition and reconstruction of the data is a softwaredeveloped by RX Solutions: X-Act. For post-processing (visualization andanalysis of porosity), the software VG Studio Max Version 2.2 was used.

Analysis showed the pore volume (Vm) for a vast majority of the materialis between 1·10⁻⁴ mm³ and 5·10⁻³ mm³ (see FIG. 1).

Considering that the pore shape can be likened to a perfect sphere, weapply the following mathematical formula:

$d_{mayen} = {\sqrt{( \frac{6 \times V_{mayen}}{\pi} )}.}$

The diameter of the material is thus calculated as between 57 and 212μm.

The macroporosity of the sample is calculated as the integral of theratio of the pore volumes identified in the sample volume. According tothis calculation method, the composite material has a macroporosity of1.44%.

Example 2 Preparation of a Composite Panel of Thickness 30 mm Accordingto the Invention 1) Preparation of a Composite of Silica Alcogel

A silica sol obtained by hydrolyzing alkoxysilane in the presence ofhydrochloric acid and then adding ammonia was poured prior to gellingonto a 250×290×30 mm³ sheet of melamine foam in a closed chamber withdimensions of 300×300×70 mm³. The solvent used was ethanol. Aftergelation, the reinforced alcogel was aged for 24 hours under a reflux ofethanol. Hydrochloric acid and hexamethyldisiloxane (hydrophobing agent)were then introduced into the chamber to completely cover the compositealcogel. The reaction medium was heated and maintained at reflux inethanol for 48 h. The reaction mixture was separated from thehydrophobic silica alcogel by percolation.

2) Obtaining a Melamine Foam Panel and Hydrophobic Silica AerogelComposite

The reinforced hydrophobic silica alcogel was placed in a microwavedryer and dried for 50 min at 50° C.

The obtained aerogel panel was 30 mm thick and had a thermalconductivity of 14.2 mW/m-K, measured by means of guarded hot plate ofNF EN 12667 at 20° C. and atmospheric pressure.

Example 3 Measurement of Flexibility of the Composite Material Accordingto Example 1

A 3-point bending test was performed as shown in FIG. 2 on a 25×10×250mm³ sample of material manufactured according to the method presented inExample 1. The composite material is placed on two supports separated by100 mm.

Different forces are applied to the sample at its center. Thedisplacement (flex) thereof was measured.

Results:

The results obtained are shown in FIG. 3. The stiffness or flexuralrigidity was calculated as K=0.0385 N/mm, which corresponds to the slopeof the force-deflection curve.

Example 4 Measurement of Maximum Compression Stress of a CompositeMaterial According to Example 1

A uniaxial compression test was performed on an electromechanicaltesting machine Zwick 100 kN, provided with an external force sensorcapacity of 5 kN·D dimensions of the sample were 30×30×10 mm³. Themoving crosshead speed is 0.3 ram/min during load and 1 mm/min duringdischarge.

The results of this test are shown in FIG. 4. A compression modulus of0.43 MPa was measured, and a maximum stress of 3.3 MPa with a relativedeformation of 80%.

Example 5 Preparation of a Composite Insulating Foam Panel 10 mm ThickAccording to the Invention 1) Preparation of a Silica Hydrogel Composite

A silica sol obtained by mixing an aqueous solution of sodium silicateand hydrochloric acid solution, was poured before gelation on a250×290×10 mm³ sheet of melamine foam in a closed chamber havingdimensions of 300×300×70 mm³. After gelling, the reinforced hydrogel wasaged for 24 hours at 50° C. in water. A solvent exchange was carried outwith acetone (for 48 h at 50° C. by recycling acetone two times).Hydrochloric acid and hexamethyldisiloxane (hydrophobing agent) werethen introduced into the chamber so as to completely cover the compositelyogel. The reaction medium was heated and maintained at 50° C. for 48h. The reaction medium as separated from the hydrophobic silica lyogelby percolation.

2) Obtaining a Composite Panel Comprising Melamine Foam and HydrophobicSilica Xerogel

The condensed lyogel reinforced by the sheet of melamine foam was driedin a ventilated oven at 160° C. for 2 hours. The xerogel panel obtainedwas 9 mm thick and has a thermal conductivity of 14.5 mW/m-K, measuredby means of guarded hot plate of NF EN 12667 at 20° C. and atmosphericpressure.

It is noted that the panels according to Examples 1, 2 and 5 allcomprise between 92% and 98% of aerogel by weight based on the weight ofthe composite.

In all the above examples, ammonia is used as a gel catalyst (step b) inan amount between 2 and 2.5% by weight relative to the total weight ofthe sol starting components.

2. Material according to claim 1, produced by a process comprising thefollowing successive steps: a) casting an inorganic sol in a reactor inwhich was previously placed a preformed open-cell melamine foam, b)gelation of the sol into a lyogel, c) drying the lyogel.
 3. Materialaccording to claim 2, characterized in that said sol used in step a)comprises more than 5% by weight, preferably between 6 and 15% byweight, of inorganic material based on the total weight of the inorganicsol.
 4. Material according to claim 1, characterized in that macroporeswhose diameter is between 50 and 250 microns comprises more than 80% oftotal macropores of said material.
 5. Material according to claim 1,characterized in that the material has a thickness of between 2 and 50mm.
 6. Material according to claim 1, characterized in that the materialhas a density between 70 kg/m³ and 150 kg/m³.
 7. Material according toclaim 1, characterized in that the melamine foam is amelamine-formaldehyde foam having a thickness of between 2 and 50 mm, aporosity of between 95% and 99.5%, a density between 8.5 and 11.5 kg/m³,and a thermal conductivity of between 35 and 40 mW/m-K measured by meansof guarded hot plate of NF EN 12667 at 20° C. and atmospheric pressure.8. Material according to claim 1, characterized in that the inorganicaerogel is selected from silica aerogels, titanium oxide, manganeseoxide, calcium oxide, carbonate calcium, zirconium oxide, or mixturesthereof.
 9. Material according to claim 1, characterized in that thematerial does not contain any binder.
 10. Material according to claim 9,characterized in that the material does not comprise a fibrousreinforcing material.
 11. Material according to claim 1, characterizedin that the material has a quantity of residual solvent by weight of thecomposite material of less than or equal to 3% according to EN/ISO 3251.12. Material according to claim 1, characterized in that the aerogelfurther comprises an opacifier.
 13. A sandwich panel comprising at leastone layer consisting essentially of a monolithic composite materialaccording to claim
 1. 14. Use of a composite material according to claim1 or of a multilayer panel according to claim 13 as thermal insulation.15. Use of a composite material according to claim 1 or of a multilayerpanel according to claim 13 as acoustic insulation.